Volvo Repair: Volvo 850 misfire, volvo dealership, oxygen sensor

Question
QUESTION: I have an 850 GLT and it began to have an issue with rough idle at cold
startup.  I changed the plugs, wires, cap, rotor and even installed a new coil.  
The problem persisted.  I then took it to the local dealership.  They changed
the Oxygen sensor and found a leaking tube on the turbo control valve.  This
also did not fix the problem.  
The actual event that occurs happens immediately at cold start.  It produces a
shudder through the car and sounds coarse accordingly.  The problem
persists for approximately 7 to 10 seconds then it stops suddenly and the car
runs perfectly fine.  I have noticed excess black soot from the tailpipe on the
garage floor.  Once in a while when running rough it will produce a code of
PO303, or misfire on cyl #3.  The volvo dealership here said they have no idea
what is wrong with it as all systems are functioning perfectly.  Their best
guess is that there is an exhaust valve sticking in cyl.#3 and until it heats up
it causes the misfire and suggested "trying" a valve job at the tune of $2000.  
What do you think?  
The car has just 100,000 miles on it and I am the original owner.

ANSWER: Daniel, to me it sounds more like a problematic Air mass meter.  What kind of cap rotor, etc, did you use?  We can go further on this one if you want. Roger

---------- FOLLOW-UP ----------

QUESTION: The cap, rotor, wires are from IPD.  The Plugs are Iridium, and the coil is MSD.  
It is important to note that this problem existed before I changed these parts
and didn't change afterward.  The service dept at the dealer said volvos are
picky about the plugs and tried putting in fresh volvo plugs and nothing
changed when that happened. They also felt very strongly that it wasn't the
MAS, they claimed that the car would exhibit the same problems consistently
and would perform poorly throughout the operating range.  It is however one
part that they did not change or swap out.

Answer
Daniel, the only other part that has anything to do with fuel is the ECT sensor.  It may be overfueling when cold causing the misfire.  The burn after the 7 to 10 seconds would smooth it out.  Other than that, I have no other suggestions without seeing the car in person.  Roger